From the New York Times synopsis:

When Anna is cursed by her estranged sister, the cold-hearted Snow Queen, Anna's only hope of reversing the curse is to survive a perilous but thrilling journey across an icy and unforgiving landscape. Joined by a rugged, thrill-seeking outdoorsman, his one-antlered reindeer and a hapless snowman, Anna must race against time, conquer the elements and battle an army of menacing snowmen if she ever hopes to melt her frozen heart.

...Disney will be inducting new Princesses, skipping over the awkward 11 and heading straight on to 12? My guess at the moment is maybe, but unlikely. Merchandising usually relies on a character's pre-film state (Rapunzel keeps her lengthy locks, Ariel is more mermaid than human, Mulan is in her hanfu, etc), so they wouldn't be able to induct the Snow Queen without spoiling that she returned to a human Princess (if that is what happens).

And after reading this new synopsis, I want a more unique ending - instead of Elsa turning human again, Anna discovers her own supernatural ability and becomes a Queen herself (Spring Queen?) to match and make peace with her sister. I'm also well-aware that idea has a snowball's chance in heck of that happening.

What's likely the plot is some sort of sibling rivalry storyline: Anna is the preferred Princess (though maybe younger) and Elsa, who wants to be Queen and feels pushed aside by her family, accepts some dark magic that allows her to curse her former kingdom and become a Queen in her own right. Anna sets off after her sister, has adventure, Elsa sees the light in her sister's determination to save her, returns to her former state, and supports or rules alongside her sister. Roll credits.

From FirstShowing:

After all of that, we got a quick glimpse at Disney's new film, Frozen, their next CG animated project that's loosely based on Hans Christian Anderson's "The Snow Queen." The musical stars Broadway legend Idina Menzel as Elsa, a queen in self-imposed exile, and Kristen Bell as her sister Anna, who, along with a mountain man named Kristoff, travels into the icy wilderness to track find her sister and bring her home. Bobby Lopez (Book of Mormon, Winnie the Pooh) and his wife Kristen are writing the songs for this movie, and along with Menzel's talents, we'll also be hearing Bell's singing voice too. (The younger actress also got her start on Broadway.)

We saw some concept art for the various characters in Frozen (a goofy enchanted snowman named Olaf and a bizarre reindeer named Sven look to be the comic relief) and some dazzling locations, like a castle nestled into a gorgeous mountain range with interior designs that had a beautiful, ethereal, classic Sleeping Beauty look to them. There were also research photos from the crew's trip to Jackson Hole, Wyoming, where they trudged through ten feet of snow to get an up close experience regarding how those motions look and feel so they can incorporate it into the film.

From IGN:

While paying a visit to Walt Disney Animation Studios for their upcoming feature Wreck-It Ralph, IGN was fortunate enough to also sneak a peek at their next project, Frozen.

When it was first announced, we learned that the CG musical film told the story of the fabled Snow Queen, loosely based on the Hans Christian Anderson fairytale. We've also known for about a month now that Kristen Bell and Idina Menzel are set to voice the lead roles. More recently, we discovered where the movie has drawn its inspiration.

"This is going to be a world that is inspired by the real, rugged, majestic beauty of Norway," said Emily Thompson, Senior Manager of Communications at Disney Animation. "Even though the story won’t necessarily take place in a specific time or location, that’s our inspiration."

At its heart, though, Frozen tells the story between two sisters, Anna (Bell) and Elsa (Menzel). "They do a really, really fantastic job together," continued Thompson. "Anna and her partner in crime, Kristoff -- he’s kind of a rugged mountain man -- they set off on a journey to find Anna’s sister the Snow Queen, Elsa, who’s banished herself to the mountains where she’s built this beautiful snow palace; she’s in this kind of self-imposed exile. So they’re going to find Elsa and bring her back."

This is all in order to save Anna's kingdom, which has been cursed in eternal winter. "Along the way, they meet up with this enchanted snow man Olaf, who provides a lot of the comic relief. Then there’s also a mangy looking reindeer named Sven."

The Disney project, which was originally shelved back in 2010, is now being helmed by Tarzan's Chris Buck, with music by Robert Lopez and his wife Kristen (Winnie the Pooh). The film is currently slated for release in November 2013.

From A Destination D recap on the DisneyPinForum by disneycrazee :

They also showed concept art along with final character designs from Frozen (formerly The Snow Queen). When I first heard months ago about the name change and the fact that they were no longer animating it traditionally, I was disappointed. I was still slightly disappointed when I saw the character design for one of the sisters, Anna, mainly because I was expecting something a little more...fantastical? But then they showed us Elsa, whose design I fell in love with immediately (and I couldn't help but think, she would make a gorgeous LE doll! lol). We were also treated to a performance of one of Elsa's songs in the movie, "Let It Go". It's a powerful ballad, and it's still in my head!

From A Destination D Review on Micechat by Disneyland 1951:

The amazing highlight was the fall 2013 movie "Frozen". They showed art, storyboards, and told much of the story. They had a live presentation of a Song from Frozen that was wonderful and moving. The background art looks great. The main characters are two beautiful princess sisters from Norway.

From A Destination D review by LaurasMiscMusings:

A preview of next year's animated musical Frozen (2013), a telling of The Snow Queen. It looks gorgeous, with some of the artwork reminiscent of Mary Blair's style. Idina Menzel of Broadway's Wicked and Disney's Enchanted (2007) voices the title role, with Kristen Bell co-starring.

Disneycrazee independently adds that the style of Anna reminds her of the Mary Blair-style short in Melody Time:

[Anna] definitely does NOT look like that, but I think it's the winter setting, the very sweet and innocent look to her that made me think of this character from Melody Time. I can say, though, that Anna looks pretty young...

Whereas Anna has a much softer look to her, Elsa is edgier, sharper. Her hair is shorter and white (or at least it appeared white to me). She has a much more regal air about her.

Kristoff's look pairs well with Anna. It's hard to remember now, but I want to say broad-shouldered while still having that "softer" look about him. Very mountain man-ish.

Olaf is a goofy little snowman. Director Chris Buck was talking to us about when you make your first pancake, it's not perfect...maybe even black on the bottom. He said Olaf is Elsa's first pancake. He has an enormous curving carrot nose, and a scrawny body that makes him look like the rest of him just melted off.

And DVDizzy member Lnds500 pointed out - remember Hans, the 'princely' character described in the last Frozen post?

Hans Christian Andersen
Hans Kristoff Anna

Big ups to Sotiris on the DVDizzy.com boards (here and here) for putting together these excerpts.